If you want the sale to go through, you'll probably have to close on or very near the agreed upon date. Since you already agreed to sell, if you do not send the paperwork back or cancel the sale at this point, you are going to owe the broker his/her commission and open up yourself to legal action by the buyer (but that's probably not very likely as most buyers will think it not worth the time or cost to go after you. Not sure what the broker might choose to do).
If you can't take the vacation as scheduled, you can certainly try to negotiate something with the buyer. If he/she wants the original deal and you want to honor the deal you made, my advice is to forget rescheduling the vacation with those points. You could try to rent the reservation. If that vacation was made with current use year points, you could try to transfer them to another member prior to the deal going to Disney for estoppel. (They will be holding points, though and will probably get quite a bit less than unrestricted points. Holding points expire at the end of the use year). If you can't use / rent /transfer the points prior to the agreed upon close date, consider them as a nice gift to the buyer & be sure to tell the buyer that they are there. Perhaps they will be able to use them.
Sorry about your situation, and hoping things resolve themselves so that you can take the vacation as scheduled. Good luck!
